Several patents and publications are cited in this description in order to more fully describe the state of the art to which this invention pertains. The entire disclosure of each of these patents and publications is incorporated by reference herein.
Architects and designers often use frosted glass to allow light into a space while affording privacy to those within the space. Sand blasting and acid etching are two ways to produce frosted glass from smooth, transparent glass lites. Frosted glass is difficult to clean and maintain, however. In addition, sand blasting and acid etching are not medically or environmentally friendly processes, because of their many waste products, and because of the risk of burns from handling acids and silicosis from inhaling the dust that results from sand blasting. As a result, laminated glass with a diffuse translucent interlayer was developed. The interlayer provides the desired optical properties, and it may be laminated between smooth glass lites that are easy to clean and maintain. Often, the diffuse translucent interlayers are based on polyvinyl butyral compositions.
Translucent white polyvinyl butyral compositions are commercially available from every major manufacturer of polyvinyl butyral. Typically, the optical properties of these compositions feature light transmission (LT) of approximately 65%; clarity of approximately 15 to 30%; and haze of 95% or higher. The commercially available polyvinyl butyral compositions include calcium carbonate as a diffusing agent. In order to achieve the desired translucent appearance, interlayer sheets having a thickness or caliper of 0.76 mm contain approximately 2.5 wt % of calcium carbonate having a particle size of around 3.5 microns.
For certain structural or high strength applications, the superior mechanical properties of ionomeric interlayers such as DuPont™ SentryGlas® are required. These structural applications include architectural features, such as stairs, balconies and balustrades, and windows and skylights that are vulnerable to damage caused by severe weather or physical attack, for example.
Further in this connection, a variety of articles made from ionomers are used in our daily life. These articles may be made by injection molding processes, for example, and include items such as containers, caps or stoppers, trays, medical devices or instruments, handles, knobs, push buttons, panels, console boxes, footwear components, figurines or other decorative articles, and intermediate articles such as pre-forms or parisons. DuPont™ Surlyn® is one type of ionomeric material that has been used in fabricating these and other articles, because Surlyn®'s physical and optical properties are superior to those of many thermoplastic materials.
Moreover, the optical properties associated with etched, ground or frosted glass may also be considered desirable in these everyday articles. A translucent white polymer composition having characteristics similar to those of Surlyn® will provide the articles with the desired appearance and physical properties. In addition, the use of a suitable translucent white polymer composition will obviate the need to tool special molds or to treat the articles' surfaces with solvents or abrasives in order to obtain the desired appearance of frosted glass.
As is discussed above, calcium carbonate is a diffusing agent commonly used in commercially available translucent polyvinyl butyral compositions. When calcium carbonate is compounded into suitable ionomeric resins, however, significant foaming is frequently observed, due to the gas produced by the chemical reaction between the ionomer and the calcium carbonate.
Another commonly used whitening agent is titanium dioxide. The average particle size of titanium dioxide is too small to achieve the desired optical effects, however, whether the glass laminate includes a polyvinyl butyral interlayer or an ionomeric interlayer. More specifically, adding titanium dioxide to the interlayer reduces its light transmission but not its clarity. Therefore, the key design function of providing privacy is not achieved.
Other pigments with relatively low indices of refraction comparable to that of calcium carbonate are available. For example, silica, alumina, talc, clay, vermiculite, glass fibers, barium sulfate, alumina trihydrate (ATH), alumina (Al2O3), magnesium oxide (periclase), beryllium aluminate, calcium sulfate, zinc phosphate tetrahydrate and mullite have been used as fillers in ionomeric compositions. In fact, alumina trihydrate (ATH) has been compounded into ionomers at high loadings of approximately 65 parts ATH to 100 parts resin to achieve fire retardancy. Handbook of Fillers for Plastics Harry S. Katz and John Milewski, eds. Springer, 1988 pg. 296 (ISBN 978-0-442-26024-8). The resulting composition is opaque, however, not translucent. Moreover, the addition of ATH to ionomer is known to create significant amounts of gel in the compounded composition.
It is apparent from the foregoing that a need exists for translucent white polymer compositions that can be used in molded articles. It is further apparent that a need exists for translucent white polymer compositions that are suitable for use as interlayers in glass laminates, including safety glass laminates, and particularly as ionomeric interlayers for the safety glass laminates that are used in structural applications or other end uses requiring superior strength or stiffness.